High temperature resistant oxidation catalyst, a process for its preparation and a combustion process using this catalyst

Abstract

A non-selective high temperature resistant oxidation catalyst and a process for the preparation of this catalyst is described. The catalyst mainly has the formula A1-xByCzAl12-y-zO19- delta , where A represents at least one element selected from the group formed by barium, strontium and the rare earths; B represents at least one element with valency Y selected from the group formed by Mn, Co and Fe; C represents at least one element selected from the group formed by Mg and Zn; x has a value of 0 to 0.25, y has a value of 0.5 to 3 and z has a value of 0.01 to 3; the sum y+z has a maximum value of 4 and delta has a value which is determined as a function of the respective valencies X and Y of elements A and B and the value of x, y and z and is equal to 1-+E,fra 1/2+EE {(1-x)X+yY-3y-z}. The catalysts of the invention are particularly for use in processes for the catalytic combustion of hydrocarbons, carbon monoxide, hydrogen or mixtures thereof.

I claim: 
     
       1. A non-selective high temperature resistant oxidation catalyst comprising a lamellar hexaaluminate of the formula A 1-x  B y  C z  Al 12-y-z  O 19- δ, where A represents barium, strontium or a rare earth with a valency X; B represents at least one element with valency Y which is Mn, Co or Fe; C represents at least one of Mg or Zn; x has a value of 0 to 0.25, y has a value of 0.5 to 3 and z has a value of 0.01 to 3; the sum y+z has a maximum value of 4 and δ has a value which substantially complies with the oxidation state of the elements in the catalyst. 
     
     
       2. A catalyst according to claim 1, wherein the atomic ratio of A to the sum B+C+Al is about 0.0625 to 0.083. 
     
     
       3. A catalyst according to claim 1, wherein element A is lanthanum or barium, element B is manganese and element C is magnesium. 
     
     
       4. A catalyst according to claim 1 wherein the values of y and z are respectively between 0.5 and 2 and between 0.01 and 2. 
     
     
       5. A catalyst according to claim 1, wherein in formula A 1-x  B y  C z  Al 12-y-z  O 19- δ  element B and element C are incorporated into the structure of the lamellar hexaaluminate. 
     
     
       6. A catalyst according to claim 1, having a specific surface area of 10 to 100 m 2  /g after calcining at 1200° C. 
     
     
       7. A catalyst according to claim 1, wherein the hexaaluminate A 1-x  B y  C z  Al 12-y-z  O 19- δ  is supported on a metallic or ceramic substrate. 
     
     
       8. A catalyst according to claim 7, wherein substrate is a monolithic material with a cellular structure. 
     
     
       9. A catalyst according to claim 1, wherein the hexaaluminate A 1-x  B y  C z  Al 12-y-x  O 19- δ  is formed into a monolithic material with a cellular structure. 
     
     
       10. A catalyst according to claim 1, further comprising a precious metal from the platinum group on the catalyst surface or incorporated into the catalyst during preparation. 
     
     
       11. A process for the preparation of a non-selective high temperature resistant catalyst according to claim 1, comprising dissolving and mixing a water and/or alcohol-soluble aluminium compound, a water and/or alcohol-soluble compound of an element A which is barium, strontium or a rare earth, a water and/or alcohol-soluble compound of an element B which is Mn, Co or Fe, and a water and/or alcohol-soluble compound of an element C which is magnesium or zinc, such that the atomic ratio of A over the sum B+C+Al is about 0.0625 to 0.083, the atomic ratio of B over the sum B+C+Al is about 0.04 to 0.2, and the atomic ratio of C over the sum B+C+Al is about 0.01 to 0.2, precipitating, hydrolysing and/or thermally decomposing to form a product in the solution, extracting the product form the solution and calcining the extracted product at a temperature greater than at least 900° C. 
     
     
       12. A preparation process according to claim 11, wherein co-precipitation is carried out by (a) preparing a mixture containing a water soluble aluminium salt, a water soluble salt of at least one element A, a water soluble salt of at least one element B, and a water soluble salt of at least one element C; (b) carrying out co-precipitation of the hydroxides or carbonates of the soluble salts used in (a); (c) drying the co-precipitate and pre-calcining between 200° C. and 650° C., and (d) calcining the product obtained at a temperature of between 900° C. and 1500° C. for 5 to 30 hours. 
     
     
       13. A preparation process according to claim 11, wherein element A is lanthanum or barium, element B is manganese and element C is magnesium. 
     
     
       14. In the catalytic combustion of hydrocarbons, carbon monoxide, hydrogen or mixtures thereof, the improvement comprising conducting the combustion in contact with a catalyst according to claim 1. 
     
     
       15. A combustion process using two catalytic zones, characterised in that the catalyst in the first catalytic zone comprises palladium and/or platinum on an alumina stabilised by at least one element selected from the group composed of barium, lanthanum, silicon and tin and in that the catalyst in the second catalytic zone is a catalyst according to claim 1. 
     
     
       16. A catalyst according to claim 1, wherein element B is manganese and element C is magnesium. 
     
     
       17. A process for the preparation of a non-selective high temperature resistant catalyst according to claim 1, comprising calcining, at a temperature effective to produce a hexaaluminate, of a precipitate, hydrolysis or thermal decomposition product of a solution comprising a water and/or alcohol-soluble compound of an element A which is barium, strontium or a rare earth, a water and/or alcohol-soluble compound of an element B which is Mn, Co or Fe, and a water and/or alcohol-soluble compound of an element C which is magnesium or zinc, such that the atomic ratio of A over the sum B+C+Al is about 0.0625 to 0.083, the atomic ratio of B over the sum B+C+Al is about 0.04 to 0.2, and the atomic ratio of C over the sum B+C+Al is about 0.01 to 0.2. 
     
     
       18. A process according to claim 11, wherein precipitating, hydrolyzing or decomposing are conducted at a pH of 7 to 12. 
     
     
       19. A process according to claim 17, wherein precipitating, hydrolyzing or decomposing to produce the decomposition product are conducted at a pH of 7 to 12. 
     
     
       20. A catalyst according to claim 1, wherein δ is determined as a function of the respective valencies X and Y of elements A and B and the value of x, y and z and is equal to 1-1/2{(1-x)X+yY-3y-z.